As the constant development of the display technology, the Thin Film Transistor Liquid Crystal Display (TFT-LCD) is widely used in mobile phones, televisions, personal digital assistants, digital cameras, notebook computers, desktop computers and other consumer electronics products because of its high quality, power saving, thin body, small size and no radiation, and becomes the mainstream in the flat panel display device.
Most of the liquid crystal displays on the present market are backlight type liquid crystal displays, which comprise a liquid crystal display panel and a backlight module. The conventional liquid crystal display panel comprises a Color Filter (CF), a Thin Film Transistor Array Substrate (TFT Array Substrate) and a Liquid Crystal Layer positioned between the two substrates. The working principle is that the light of backlight module is reflected to generate images by applying driving voltages to the two substrates for controlling the rotations of the liquid crystal molecules.
At present, in order to improve the aperture of the LCD display panel and to reduce the parasitic capacitance effect, more and more liquid crystal display panel products integrates the color filter on the side of the array substrate, i.e. utilizing the COA (Color Filter On Array) technology. The COA type array substrate does not need to take into account the deviation of the cell process as being compared to setting the color filter and the black matrix on the color filter substrate according to prior art. It can appropriately reduce the width of the black matrix by ensuring that the black matrix can shield the structure, which needs light shielding, such as the gate lines, the data lines and the thin film transistor units, thereby increasing the aperture ratio.
As shown in FIG. 1, in the COA type array substrate, a protective layer 100, a color filter layer 200, pixel electrodes 300 and a black matrix (not shown) are stacked on the array of the thin film transistors T10 in order, and through holes 201 are formed on the color filter layer 200 to achieve the electrical connection between the pixel electrodes 300 and the metal material signal lines. In the actual production process, the through holes 201 in the color filter layer 200 are formed by using a pattern of a mask with a negative photoresist. The characteristic of the negative photoresist is that the area where the light is irradiated is not removed by the developer, and the area not irradiated by the light will be removed by the developer, which is opposite to the characteristic of the positive photoresist.
As shown in FIG. 2, the conventional pattern of the mask for forming the through holes 201 in the color filter layer 200 is a solid circular light shielding region 900 and a hollow light transmission region 901 outside the light shielding region 900. The solid circular light shielding region 900 corresponds to the position of the through hole 201 in the color filter layer 200. However, as shown in FIG. 3, the use of the conventional mask to produce the through hole 201 in the color filter layer 200 causes the thickness and the gradient of the color filter layer 200 at the through hole 201 to be less easily controlled and the taper is steep, which can easily cause the pixel electrode 300 in the through hole 201 to break to result in the poor electrical connection between the pixel electrodes 300 and the metal material signal lines and then, the display failure. To ensure the good electrical connection requires the production of larger through holes 201, which will undoubtedly reduce the pixel aperture ratio. Moreover, the condition of too large through hole 201 can easily lead to the gas leakage due to vibration after the cell process and may spread to the liquid crystal layer, resulting in bubble and the formation of black groups to affect the display effect.